Although various types of micromechanical substrates can be used, the present invention and the problem underlying it are explained on the basis of wafer substrates on silicon basis.
In the related art, e.g., in US 2008/0283990 A1, eutectic bond connections between substrates are described, for which aluminum/silicon/copper are used.
U.S. Pat. No. 7,442,570 B2 discusses a method for bonding two silicon substrates, in which an aluminum layer (not further described) is provided on an oxide layer, which is situated on a top surface of the substrate. This aluminum layer is eutectically bonded to a germanium layer situated on a further substrate. No aluminum spiking occurs in this process.
It is already known from the field of microelectronics to use aluminum with added silicon and copper for aluminum circuit tracks. Copper increases the current-carrying capacity of the circuit tracks, that is to say, improves the electrical migration resistance, while the addition of silicon is to prevent the known Al-spiking into the substrate. The formation of undesired aluminum spikes into the silicon substrate occurs mainly during thermal treatments, which are meant to improve/reduce the electrical contact resistance between aluminum circuit tracks and contact points of electrical components in the silicon substrate. Flat pn-junctions may be short-circuited in the process, which ultimately may lead to a breakdown of the component.
The spiking is a migration process of silicon and aluminum atoms, i.e., aluminum atoms migrate to the silicon substrate, while silicon atoms migrate to the aluminum. To prevent this behavior, normally, in the case of aluminum circuit tracks, silicon is added in the amount needed to reach the solubility limit thereof in aluminum. In practice this is achieved in that aluminum-silicon-copper targets suitable for sputtering are used during the deposition process of the aluminum circuit track layer.